In an aircraft cabin, an aircraft air conditioning system known, for example, from DE 10 2006 016 541 A1 or WO 2007/115811 A1, ensures a necessary air exchange, control of the cabin temperature and cabin pressurization. The cabin internal pressure is controlled by a cabin pressure control system which comprises controllable air outlet valves arranged in the area of a skin of the aircraft fuselage. The cabin pressure control system usually comprises at least one outflow valve. Typically, the cabin pressure control system of a modern passenger aircraft is equipped with two or more outflow valves being disposed in a forward and an aft belly region of the aircraft.
During flight operation of the aircraft, the cabin pressure is adjusted as needed by appropriately controlling an effective outflow area of the at least one outflow valve. During ground operation of the aircraft, the outflow valve is fully opened in order to allow an equalization of the pressure within the aircraft cabin and the ambient pressure prevailing outside of the aircraft. In particular, the outflow valve usually is designed so as to ensure that, when the aircraft is on the ground, a residual differential pressure between the pressure within the aircraft cabin and the ambient pressure does not exceed 2 hPa. The pressure control function of the outflow valve during ground operation of the aircraft is decisive for the design of the outflow valve, in particular the maximum effective outflow area of the outflow valves and thus the overall size and weight of the outflow valves.
The cabin pressure control system further comprises at least one negative relief valve. The negative relief valve is opened in order to allow ambient air entering the aircraft cabin if, during flight operation of the aircraft, for example during a fast decent of the aircraft, the ambient pressure exceeds the cabin pressure. During ground operation of the aircraft, the negative relief valve has no function and is kept shut.